Preparation of tetramethyl lead



United States Patent 3,188,332 PREPARATION OF TETRAMETHYL LEAD Paulhlohetz and Francis M. Eeaird, Jr., Baton Rouge, La, ass-ignore to EthylCorporation, New York, N.Y., a corporation of Virginia No Drawing. FiledMay 29, 1963, Ser. No. 284,092 8 Claims. ((21. 260-437) This inventionrelates to the manufacture of alkyllead compounds. More particularly,the invention relates to a new and improved process for the synthesis ofa tetramethyllead product.

It has long been known that the tetraalkyllead compounds can be made,generally, by the reaction of an alkali metal lead alloy and an alkylhalide, particularly, the mono sodium lead alloy, NaPb and thecorresponding alkyl chloride. This type of synthesis reaction has beenemployed for an appreciable period for making large amounts oftetraethyllead. The chemical reaction is operative for othertetraalkylleads, and recently considerable interest has developed in themanufacture and use of tetramethyllead, which is an appreciably morevolatile lead antiknock compound.

Although the indicated chemical reaction, applied to the manufacture oftetramethyllead is operative, it is not too effective insofar as yieldsare concerned, relative to the type of results which can be achievedwith tetraethyllead. In addition, the synthesis of tetramethylleadpresents much more drastic control requirements, and requires morerigorous control than the corresponding type of synthesis oftetraethyllead, because of the substantially higher vapor pressure oftetramethyllead and of the methyl chloride used in its synthesis. Asubstantially improved procedure for the synthesis of tetrainethylleadis disclosed in US. Patent 3,049,558 by Cook et al. According to theCook et al. process, a controlled quantity of a class of inert liquidhydrocarbons, provides, in the presence of a catalyst, appreciablygreater yields than is achieved when no inert hydrocarbon is present.The hydrocarbons generally are those having an atmospheric boiling pointof about 90-l50 C. and these are employed in relatively smallconcentrations based on the lead in the alloy charged. Aluminum typecatalysts are highly effective catalysts.

According to the Cook et al. process, yields of the order of 60-75percent can be obtained, in reaction periods of less than about sevenhours.

The foregoing improved process has been quite successful, but even withthe improvement therein obtained, it is evident that considerable roomfor additional improvement has subsisted. Thus, even a yield of 60 to 70percent, although higher than previously obtained, obviously allowsample room for improvement, especially when it is considered that in thereaction involved, even a 100 percent yield would result in release ofabout three-fourths of the lead as excess or by-product metallic leadwhich is necessarily recovered, ire-alloyed, and, normally, re-used.

Another problem encountered in tetramethyllead synthesis is frequentdifficulty in discharge of reaction mass from commercial scaleautoclaves. By reaction mass is meant the mixture of materials presentin a reaction zone or autoclave at the termination of reaction whichmixture includes the aforementioned subdivided lead, the tetramethylleadproduct, alkali metal chloride, minor amounts of non-reacted chloride,and trace impurities or additives. Also present in the reaction mass, isthe inert hydrocarbon customarily employed. The major component of thereaction mass is subdivided lead, owing to the above mentionedstoichiometry of the synthesis reaction. The reaction mass resembles agranular mixture and is discharged from autoclaves by rotation ofagitator devices having plow elements for transport of the reaction massto a discharge nozzle or valve. In the course of commercial operations,considerable difficulty has frequently been encountered in this respect.Another difiiculty has arisen from the fact that, using aluminum typecatalysts, apparently the reaction mass also contains a residual amountof active alkyl-aluminum components which is quite susceptible tooxidation or other reaction. This is manifested by forming or smoking ofthe reaction mass when exposed to gaseous atmospheres, even when uchatmospheres are relatively free of oxygen. Such fuming necessitates theextensive use of particularly pure inert gas to partly alleviate theproblem. The fuming or smoking is especially disadvantageous in thatsuch fumes appear to deposit solids in subsequent heat exchangerequipment, which significantly fouls and reduces the capacity of suchequipment.

An object of the present invention is to provide a new and improvedprocess for the manufacture of tetramethyllead. A particularly object isto provide a novel catalyzed process for the synthesis oftetramethyllead whereby excellent yields are obtained and whereby thefuming or smoking tendency of the reaction masses produced aresubstantially minimized.

In the most general form, the present invention comprises reacting analkali metal lead alloy with methyl chloride, and in the presence of acatalyst system including an aluminum catalyst and a cyclic diether ofthe meta dioxane type. The aluminum catalyst is most frequently ahydrocarbon aluminum compound, as discussed more fully below. However,aluminum trihalides and aluminum metal can be provided for this purpose.

The hydrocarbon aluminum compounds employed are, generally, any aluminumcompound having at least one hydrocarbon radical per aluminum atom.Typical hydrocarbon aluminum compounds which are suitable includetrimethyl aluminum, triethyl aluminum, ethyl aluminum sesquichloride,methyl aluminum sesquichloride, diethyl aluminum chloride, ethylaluminum dichloride, tri-n-propyl aluminum, tri-n-butyl aluminum,triisobutyl aluminum, diisobutyl' aluminum hydride, triphenyl aluminum,trioctyl aluminum, diethyl aluminum hydride, and tridecyl aluminum. Themost generally used catalysts are, then aluminum compounds having atleast one hydrocarbon radical of from one to about ten carbon atoms. Thesimpler alkyl aluminum compounds, such as mentioned illustrativelyabove, are preferred. When desired, the hydrocarbon aluminum catalystcomponent can be generated in situ, as, for example, by the reaction ofan aluminum trihalide with a hydrocarbon compound of another metal.Thus, the reaction of aluminum trichloride and tetraethyllead willgenerate hydrocarbon aluminum moieties operative as this catalystcomponent.

As indicated, the second component of the improved catalyst system is acompound of the meta-dioxane type, viz., meta dioxane as such, andnumerous hydrocarbon substituted derivatives thereof. Examples of suchadditional catalyst components are: 4,4-dimethyl-m-dioxane;4-methyl-m-dioxane; 4-ethyl-5-methyl-m-dioxane; 4,4,5-trimethyl-m-dioxane; 4,4,5 ,S-tetrarnethyl-m-dioxane; 2,4,4, 6tetramethyl-m-dioxane; 4-methyl-4-phenyl-m-dioxane; 4-phenyl-m-dioxane;5-methyl-4-phenyl-m-dioxane; 4-vinyl-m-dioxane; 1,3,7-trioxadecalin;4,4-dimethyl-2,6-diphenyl-m-dioxane; 4,4-dimethyl-m-dioxane;2,4,4,5,6-pentamethyl-m-dioxane; S-tert-buty1-4,4-dirnethyl-m-dioxane;and 5-ethyl-4-phenyl-m-dioxane.

Various operating procedures are permissive for carrying out anyparticular embodiment of the process. In general, batch or cyclictechniques are preferred. According to such techniques, a reaction zoneis charged with subdivided solid sodium lead alloy, usually themonosodium lead alloy although some variation from this is permissive..Then the catalyst components are charged, usually in conjunction with aminor quantity of an inert hydrcarbon material, generally in theproportions of about arsaasz four or five to about twenty weight percentof the lead in the alloy. The catalyst system, as already indicated,includes in all instances, an aluminum catalyst in conjunction'with themeta-dioxane catalyst adjuvant.

Several different modes of introducing the catalyst system to thereaction zone are available. A preferred mode of addition involvesproviding both the aluminum and the meta-dioxane catalyst components infull at the beginning of the reaction.

As already stated, the initial charge usually includes an inerthydrocarbon liquid in limited proportions. The hydrocarbon is highlybeneficial in that high yields are realized at lower pressures thanwould be encountered in the absence of the hydrocarbon and the thermalstability of the product is improved. Preferably, the hydrocarbon is anaromatic type liquid, commercial toluene being a particularly beneficialexample.

After the above described charge, the reactor is sealed, except fornecessary venting connections, the temperature is raised to, usually 65or above, while the system is agitated, and methyl chloride is charged.The methyl chloride in some cases is charged all at one time, and inother cases is fed in over a deliberate finite period. The total methylchloride is provided in proportions of at least one stoichiometricrequirement or theory, and usually, a substantial excess is used. Itwill be understood that this refers to the total quantity fed duringbatch operations. During portions of such cyclic operations, only minorquantities of methyl chloride may be present, when the feed is spreadout over a finite period.

The materials thus charged together are then reacted at temperaturesaveraging from about 85 to 110 C. Agitation is provided throughout thereaction period, as the reacting system includes solids and volatileliquids. The reaction is continued to completion, requiring from aboutone hour and less than seven hours, dependent on the configuration ofthe apparatus, the degree of agitation, and the quantity of alloy to bereacted.

On completion of the reaction, the autoclave and con-.

tents are cooled and discharged, and the tetramethyllead is recoveredfrom the lead and alkali metal chloride components of the reaction mass.When small portions of hydrocarbon additive are employed in thesynthesis reaction, the tetramethyllead is usually accompanied onrecovery by said hydrocarbon liquid. As already described, in all casesan aluminum catalyst plus a meta-dioxane catalyst adjuvant is employed,the latter being selected from the group consisting of metadioxane andhydrocarbon substituted meta-dioxanes. The aluminum catalyst is providedin proportions of 0.02 to about 0.3 weight percent aluminum content,based on the sodium lead alloy used. A preferred range is from about0.04 to 0.25 weight percent, an even more preferred range being 0.08 to0.15 weight percent aluminum. The precise proportions of the aluminumcatalyst in any specific example depends, of course, on the compositionand molecular weight thereof.

With respect to the meta-dioxane type component, its ratio to thealuminum component is not highly critical. Highly efiective results areobtained from about one-tenth to as high as fifteen moles per atom ofaluminum in the aluminum catalyst. Lower and higher proportions can beused, with appreciably less benefit, or with no supplemental benefits,respectively. It will be appreciated that the concentrations throughoutthe range are in catalytic proportions, owing to the low concentrationsof the aluminum catalyst. A preferred proportion of the meta-dioxanecomponent is from about one-fourth to five moles per. atom of aluminum,an even more preferred range being from about one to three moles pergram atom.

The present invention results in the attainment of high ultimate yields,frequently higher than normally encountered. Other benefits are alsorealized. For comparison purposes, a series of base line or normaloperations 4. were conducted to provide a reference basis for contrastwhen following the procedure of the present invention.

An autoclave was charged with 1,000 parts of comminuted monosodium leadalloy, containing 10 weight percent sodium. A mixture of an aluminumtype catalyst, dissolved in anhydrous toluene was then charged, whileagitating the contents of the autoclave. The said solution was providedin proportions of about 54 parts toluene by weight, and the aluminumcatalyst was charged in proportions of about 0.24 weight percentaluminum content based on the alloy charged. According to the identityof the aluminum catalysts, of course, the weight of the catalystcompound would be varied. Thus, in the case of using methyl aluminumsesquichloride, (CH Al Cl as the aluminum catalyst, a typicalconcentration was about 0.93 weight percent of the sodium lead alloycharged.

The charge thus established was then sealed in the autoclave andpreheated to about C., and then methyl chloride was fed to the autoclaveinterior. The temperature was controlled below about C., and the methylchloride was fed during a period of less than about 30 minutes inproportions corresponding to 1.7 theories, or about 370 parts by weightper 1000 parts of the alloy charged.

Upon completion of the reaction, after reaction for a period ofapproximately two hours, the contents of the autoclave were cooled andremoved from the interior. The amount of tetramethyllead produced wasdetermined by extracting from the reaction mixture, or reaction mass,with a hydrocarbon solvent, with titration of the tetramethyllead by aniodine analysis of an aliquot of the liquid extract. Alternatively, insome instances, the reaction mass was subjected to steam distillation,for separation of the tetramethyllead from the excess lead powder andsodium chloride component of the reaction mass.

A series of operations as above described was carried out, using theprocedure indicated and with occasional slight variation in the amountof catalyst provided. Using triethyl aluminum as the catalyst, theaverage yield obtained was 77.9 percent, and when using methyl aluminumsesquichloride as catalyst in comparable concentrations, the averageyield was 76.8 percent.

The reaction mass attained in the above described base line runs wasquite reactive, in that, when portions were exposed to the. availablenitrogen gas supply as an atmosphere, considerable smoking occurred. Inaddition fre- 'quent difficulty was encountered in discharging theautoclave in that the reaction mass was sticky and gummy and tended toadhere to the vessel walls and agitator.

Example 1 In this operation, a similar procedure to the base lineoperations was followed, except that the aluminum catalyst, in thiscase, methyl aluminum sesquichloride, was reduced to proportions of 0.46weight percent, based on the alloy, and in addition meta-dioxane wasconcurrently charged, at a concentration of about 1.03 weight percent ofthe alloy. This corresponds to an aluminum concentration of 0.12 weightpercent of the alloy, and the metadioxane in proportions of 2.6 molesper atom of aluminum. Upon-completion of the reaction, it was found thata yield of 91.1 percent of tetramethyllead was obtained, representing ayield improvement of 14.3 percent above the results obtained accordingto the base-line procedure. In addition, inspection of the reaction massproduced by the process showed that it was not sticky or lumpy, andcould be readily discharged from the autoclave. The reaction mass alsowas superior in not exhibiting any fuming or smoking when contacted witha gaseous atmosphere. 7 In the foregoing, example, as indicated, thealuminum catalyst plus the meta-dioxane was added at the same time. Inother operations, alternative modes of introducing the dual catalystcomponents have been employed. These include the following:

Reverse addition:. The synergistadditive, or the metadioxane compound isadded first, and thereafter'the aluminum catalyst is provided.

Premixed addition: In this operation, the aluminum catalyst, thesynergist of the present invention, and a hydrocarbon are mixed togetherprior to adding to the autoclave charge.

In other instances, the catalyst system, viz., the aluminum alkyl plusthe synergist, are added in increments spaced apart by an appreciablelength of time, but within the first 15 minutes of reaction.

To illustrate the scope of the present invention more fully, additionalworking examples are given below:

Example 2 The procedure of Example 1 was repeated, except that theamount of meta-dioxane was lowered to a concentration of 0.4 Weightpercent of the alloy charged. A yield of 80.9 percent tetramethylleadwas obtained, corresponding to a yield improvement of about 4 percenteven though the concentration of the methyl aluminum sesquichloride wasonly about one-half that used in the base line runs. In addition, thereaction mass was nonfuming when exposed to a gaseous atmosphere, andwas readily discharged from the reactor.

Both of the foregoing examples employed normal catalyst addition, i.e.,using premixed toluene and the methyl aluminum sesquichloride, and theco-catalyst, fed entirely at the start of the operation. The followingexample describes an operation in which a delayed addition was used.

Example 3 The operations of Example 2 were repeated, except that in thiscase, the meta-dioxane was mixed with and added initially with aboutone-third of the toluene employed. A short period later, the methylaluminum sesquichloride, dissolved in the remainder of the toluene, wascharged. This operation provided a good yield, although not as high asin Examples 1 and 2, and a longer induction period was encounteredbefore reaction proceeded at a good rate.

The examples following illustrate further the scope of the process.

Aluminum Component Meta-Dioxane Component Example Concen- Moles/ trationgm. Identity as Al, Wt. Identity Atom percent of Al 01 Alloy (C4H9)3Al0. O5 i-methyl-m-dioxane- 4. 8 (CwH2O2AlH 0. 30 4,4,5-trimethyl-m- 3. 2

dioxane. Al Metal 0. 23 2,4,4,6-tetrarnethyl- O. 25

m-dioxane. (C 11 AlH 0. O8 4-phenyl-m-dioxane 8. 1 AlCla 0. 09l,3,7-tri-xadeealin l. (iCiHs) 3A1- 0. 14 4,5-dimethy1-m- 2. 8

dioxane. (CzHs) 3A1 0. 03 5-t-butyl-4A- 4. 5

dimethyl-mdioxane. 11 (C2H5) Al2Cls i U. 11 2,4,4,5,6-penta- 2. 6

methyl-mdioxane. 12 (CgHzJ AlOl 0. l2 4,4dirnethyl-2,G- 2. 5

diphenyl-mdioxane. 13 (C2H5)A1Clz 0. 11 fi-methyl-tphenyl- 1. 1

m-dioxane. 14 (11CaH7)aA1 U. 12 4-ethyl'5-methyl-m- 1. 1

dioxane.

When carrying out the foregoing operations, good yields Will be obtainedand reaction masses will be obtained which are readily discharged fromthe reactor and exhibit little or no turning.

In addition to the aluminum catalyst specifically illustrated above,other aluminum catalysts will be readily apparent to one skilled in theart. Accordingly, when any of the foregoing examples are repeated,similar results will be achieved by replacing the aluminum catalyst withanother as used in a different example, or as previously illustrativelylisted. It will be readily apparent that, in the case of the aluminumcatalysts having a plurality of hydrocarbon groups, such groups need notbe identical. Thus, for example, a catalyst having the compositionhexylbutyl-ethyl aluminum would be quite eflective. Similarly, insteadof the alkyl aluminum chloride components, corresponding alkyl aluminumbromides or iodides can be substituted at least in part and willsimilarly function in the improved process. Further, it should beunderstood that the known complexed alkyl aluminum compounds can beemployed as aluminum catalyst components. Illustrative of additionalaluminum catalysts which can be substituted in the foregoing examplesare alkali metal aluminum tetraalkyls or trialkyl hydrides, or thealkali metal aluminum alkyl halides. Thus, sodium aluminum tetraethyl,sodium aluminum triethyl hydride, lithium aluminum triethyl hydride, andsimilar complexes can effectively be substituted for the aluminumcatalyst identified in the foregoing examples.

In addition to the explicit meta-dioxane components illustrated in theexamples identified above, when 4,4-dimethyl-m-dioxane;4,4,5,5-tetramethylm-dioxane; 4-methyl-4-phenyl-m-dioxane;4-vinyl-m-dioxane; l,3-dioxadecalin; 4 methyl 4 vinyl m dioxane; 2,4dimethylm-dioxane; and 5-ethyl-4-phenylrndioxane are individuallysubstituted for the meta-dioxane component in the foregoing examples,compaarble results are achieved. It will also be understood that whendesired, the meta-dioxane component can include several compounds of thedescribed class.

Having tully described the improvement of the present invention and thebest mode of performing the process, what is claimed is:

1. The process of manufacture of tetramethyllead comprising reacting asesscn-tially the sole reactants a sodium lead alloy and methyl chloridein the presence of a catalyst system formed by adding an aluminumcatalyst and at least one co-catalyst which is an organic compound consisting of carbon, hydrogen and oxygen, the aluminum catalyst beingselected from the group consisting of aluminum,

aluminum trichloride,

aluminum tribromide,

aluminum triiodide, and

a hydrogen aluminum "compound having at least one hydrocarbon groupbonded to aluminum by a carbon-aluminum linkage and selected from thegroup consisting of trihydrocarbon aluminum compounds, hydrocanbonaluminum chlorides, hydrocarbon aluminum hydrides, and hydrocarbonaluminum alkoxides, wherein the said hydrocarbon groups bonded toaluminum are hydrocarbon groups selected from the group consisting ofalkyl, phenyl and mixtures thereof, said cocatalyst being a compoundselected from the group consisting of meta-dioxane and hydrocarbonsubstituted meta-dioxane, the hydrocarbon radicals of the saidcocatalyst being radicals selected firom the group consisting of alkyl,phenyl, and mixtures thereof.

2. The process of manufacture of tetramethyllead comprising reacting asessentially the sole reactants a sodium lead alloy and methyl chloridein the presence of a catalyst system formed by adding an aluminumcatalyst and at least one co-catalyst which is an organic compoundconsisting of carbon, hydrogen and oxygen, the aluminum catalyst beingselected from the group consisting of aluminum,

aluminum trichloride,

aluminum tribromide,

aluminum triiodide, and

a hydrogen aluminum compound having at least one hydrocarbon groupbonded to aluminum by a carbonaluminum linkage and selected from thegroup consisting of trihydrocanbon aluminum compounds, hydrocarbonaluminum chlorides, hydrocarbon aluminum hydrides, and hydrocarbonaluminum alkoxides, wherein the said hydrocarbon groups bonded toaluminum are hydrocarbon groups selected from the group consisting ofalkyl, phenyl and mixtures thereof, said co-catalyst being meta-dioxane.

3. The process of manufacture of tetramethyllead comprising reacting asessentially the sole reactants sodium lead alloy with methyl chloride inthe presence of a catalyst system formed by adding an alkyl aluminumcompound and a meta dioxane compound selected from the group consistingof meta dioxane and an alkyl substituted meta dioxane, the alkylaluminum compound being in a concentration providing from about 0.02 to0.3 Weight percent aluminum based on the alloy and the meta dioxanebeing in proportions of from about one-fourth t0 five moles per gramatom of the aluminum.

4. The process of claim 3 in which the alkyl aluminum compound is atrialkyl aluminum.

5. The process of claim 4 in which the trialkyl aluminum is triethylaluminum.

6. The process of claim 3 in which the alkyl aluminum compound is analkyl aluminum chloride.

7. The process of claim 6 in which the alkyl aluminum chloride is methylaluminum sesquichloride. 8. A reaction mass derived from the reaction ofa sodium lead alloy and methyl chloride as essentially the solereactants in the presence of a catalyst and reaction system including aninert hydrocarbon liquid, an aluminum catalyst, and a meta-dioxanecompound selected from the 'group consisting of meta dioxane andhydrocarbon substituted meta-dioxane, said reaction mass beingcharacterized by the relative freedom from fuming and smoking whenexposed to gaseous atmospheres having smoke initiating reactantstherein, the hydrocarbon radicals of the said hydrocarbon substitutedmeta-dioxane 'being radicals selected from the group consisting ofalkyl, phenyl, and mixtures thereof.

References tilted by the Examiner UNITED STATES PATENTS 2,905,646 9/59Natta et al 252-431 2,989,487 6/61 Truett 252-431 3,052,702 9/62Robinson 260437 3,057,897 10/62 Robinson 260-437 3,072,694 1/63 Tullio260--437 3,072,695 1/63 Tullio 260437 TOBIAS E. LEVOW, Primary Examiner.

1. THE PROCESS OF MANUFACTURE OF TETRAMETHYLLEAD COMPRISING REACTING ASESSENTIALLY THE SOLE REACTANTS A SODIUM LEAD ALLOY AND METHYL CHORIDE INTHE PRESENCE OF A CATALYST SYSTEM FORMED BY ADDING AN ALUMINUM CATALYSTAND AT LEAST ONE CO-CATALYST WHICH IS AN ORGANIC COMPOUND CONSISTING OFCARBON, HYDROGEN AND OXYGEN, THE ALUMINUM CATALYST BEING SELECTED FROMTHE GROUP CONSISTING OF ALUMINUM, ALUMINUM TRICHLORIDE, ALUMINUMTRIBROMIDE, ALUMINUM TRIODIDE, AND A HYDROGEN ALUMINUM COMPOUND HAVINGATG LEAST ONE HYDROCARBON GROUP BONDED TO ALUMINUM BY A CARBON-ALUMINUMLINKAGE AND SELECTED FROM THE GROUP CONSISTING OF TRIHYDROCARRBONALUMINUM COMPOUNDS, HYDROCARBON ALUMINUM CHLORIDES, HYDROCARBON ALUMINUMHYDRIDES, AND HYDROCARBON ALUMINUM ALKOXIDES, WHEREIN THE SAIDHYDROCARBON GROUPS BONDED TO ALUMINUM ARE HYDROCARBON GROUPS SELECTEDFROM THE GROUP CONSISTING OF ALKYL, PHENYL AND MIXTURES THEREOF, SAIDCOCATALYST BEING A COMPOUND SELECTED FROM THE GROUP CONSISTING OFMETA-DIOXANE AND HYDROCARBON SUBSTITUTED META-DIOXANE, THE HYDROCARONRADICALS OF THE SAID COCATALYST BEING RADICALS SELECTED FROM THE GROUPCONSISTING OF ALKYL, PHENYL AND MIXTURES THEREOF.